Pulsed discharge jet electronic spectroscopy of the aluminum dicarbide (AlC2) free radical.

Laser-induced fluorescence and wavelength resolved emission spectra of the C ̃(2)B(2)-X̃ (2)A(1) band system of the gas phase aluminum dicarbide free radical have been obtained using the pulsed discharge jet technique. The radical was produced by electron bombardment of a precursor mixture of trimethylaluminum in high-pressure argon. The three vibrational frequencies of T-shaped AlC(2) have been determined in both the combining states along with several of the anharmonicity constants.

High resolution study of spin-orbit mixing and the singlet-triplet gap in chlorocarbene: stimulated emission pumping spectroscopy of CH(35)Cl and CD(35)Cl.

We report on high resolution studies of spin-orbit mixing and the singlet-triplet gap in a prototypical halocarbene, CHCl, using stimulated emission pumping (SEP) spectroscopy from the A (1)A(") state. Results are reported for two isotopomers, CH(35)Cl and CD(35)Cl. We have obtained rotationally resolved spectra for the majority of X (1)A(') levels lying between 0 and 6000 cm(-1) above the zero-point level that were previously observed under low resolution in single vibronic level emission studies and several new levels that were previously unobserved or unresolved.

High resolution probe of spin-orbit coupling and the singlet-triplet gap in chlorocarbene.

Among the most important of chemical intermediates are the carbenes, characterized by a divalent carbon that generates low-lying biradical (triplet) and spin-paired (singlet) configurations with unique chemical reactivities. The "holy grail" of carbene chemistry has been determining the singlet-triplet gap and intersystem crossing rates. We report here the first high resolution spectra of singlet-triplet transitions in a prototypical singlet carbene, CHCl, which probe in detail the triplet state structure and spin-orbit coupling with the ground singlet state.

Single vibronic level emission spectroscopic studies of the ground state energy levels and molecular structures of jet-cooled HGeBr, DGeBr, HGeI, and DGeI.

Single vibronic level dispersed fluorescence spectra of jet-cooled HGeBr, DGeBr, HGeI, and DGeI have been obtained by laser excitation of selected bands of the A (1)A(")-X (1)A(') electronic transition. The measured ground state vibrational intervals were assigned and fitted to anharmonicity expressions, which allowed the harmonic frequencies to be determined for both isotopomers. In some cases, lack of a suitable range of emission data necessitated that some of the anharmonicity constants and vibrational frequencies be estimated from those of HGeClDGeCl and the corresponding silylenes (HSiX).

An optical-optical double resonance probe of the lowest triplet state of jet-cooled thiophosgene: rovibronic structures and electronic relaxation.

The vibrational structure, rotational structure, and electronic relaxation of the "dark" T1 3A2(n,pi*) state of jet-cooled thiophosgene have been investigated by two-color S2<--T1<--S0 optical-optical double resonance (OODR) spectroscopy, which monitors the S2-->S0 fluorescence generated by S2<--T1 excitation. This method is capable of isolating the T1 vibrational structure into a1, b1, and b2 symmetry blocks. The fluorescence-detected vibrational structure of the Tz spin state of T1 shows that the CS stretching frequency as well as the barrier height for pyramidal deformation are significantly greater in the 3A2(n,pi*) state than in the corresponding 1A2(n,pi*) state.

Contribution to the analysis of the predissociated rovibronic structure of the symmetric isotopomers 16O3 and 18O3 of ozone near 10,400 cm-1): [3A2(3(2)(0)) <-- X1A1(0(0)(0))] and 3B2 <-- X1A1.

The absorption spectrum of ozone was recorded at low temperatures (down to -135 degrees C) by high resolution Fourier transform spectrometry and intra cavity laser absorption spectroscopy (ICLAS) near 10,400 cm-1. A preliminary analysis of the rotational structure of the absorption spectra of 16O3 and 18O3 shows that this spectral region corresponds to a superposition of two different electronic transitions, one with a very broad rotational structure, showing for the first time the asymmetric stretching frequency mode nu3 of the electronic state 3A2, the other formed by a completely diffuse band, probably the 2(1)(0) band of a new transition due to the triplet electronic state 3B2. Predissociation effects induce large broadening of the rotational lines for the transition centered at 10,473 cm-1 identified as the 3(2)(0) band of the 3A2 <-- X1A1 electronic transition.

Spectroscopy and predissociation of the 3A2 electronic state of ozone 16O3 and 18O3 by high resolution Fourier transform spectrometry.

A high resolution Fourier transform spectrometry analysis of the rotational structure of the 2(0)1 absorption bands of the 3A2<--X1A1 Wulf transition for the isotopomers 16O3 and 18O3 of the ozone molecule is presented. These bands are very intense compared to the 0(0)0 bands but the predissociation is so strong that the main sub-bands appear as continuous contours. Isolated lines and band contour methods are used together to analyse these two rovibrational bands.

Analysis of the High-Resolution Rotational Structure of the Origin and First Torsional Members of the 267-nm Band System of Formic Acid.

The fluorescence excitation spectrum of formic acid monomer (HCOOH) was recorded in the 268-257 nm region under relatively high resolution. The cooling conditions of a rotating slit-jet nozzle simplified the rotational structure and allowed for a combination line-by-line least-squares/band-contour analysis and the determination of the rotational constants. The 0(0)(0) and 9(1)(0) bands were each simultaneously fitted to a combination of c-type and b-type bands.

A Study of the Higher Electronic Transitions of Selenoformaldehyde, CH2Se.

The pi --> pi* and n --> 5s absorption spectra of selenoformaldehyde, CH2Se and CD2Se, are reported. Both spectra are diffuse. The pi --> pi* transition extends from 243 to 210 nm with an extensive Franck-Condon profile and intensity maximum estimated at 230 nm.

Contribution to the Analysis of the 3A2 <-- &Xtilde;1A1 "Wulf" Transition of Ozone by High-Resolution Fourier Transform Spectrometry.

The analysis of the rotational structure of the high-resolution Fourier transform 0(0)0 absorption spectrum of the 3A2 <-- &Xtilde;1A1 band system of the "Wulf" transition of the isotopomer 16O3 of ozone is reported for the first time. With a near pure case (b) coupling model for the upper triplet state, we have assigned a significant portion of the spectrum, mainly the F1 (J = N + 1) and F2 (J = N) spin components, primarily in the lower frequency region of the band. The lines corresponding to the F3 (J = N - 1) component are weak at lower frequencies and heavily congested in the central and higher frequency regions of the spectrum.

The Torsion-Inversion-Bending Energy Levels in the S1(n, pi*) Electronic State of Acetaldehyde.

The band assignments and analyses of the jet-cooled high-resolution laser-induced fluorescence excitation spectrum of acetaldehyde that results from the S1(n, pi*) electronic state have been extended to +600 cm-1 from the 0(0)0 system origin. The new assignments start at Band #7 and finish at Band #21. Bands #8 and #9, originally assigned to 14(2)0, have now been assigned to 15(3)0.

Rotational Analysis of the 210 and 220 Bands of the ã 3B1 <-- &Xtilde; 1A1 System of Jet-Cooled Silicon Difluoride.

A combination least-squares and band contour analysis of the 2(1)0 and 2(2)0 bands of the laser-induced phosphorescence spectrum of the ã 3B1 <-- &Xtilde; 1A1 band system silicon difluoride, SiF2, has been completed. Spectra were taken under pyrolysis-jet conditions at a resolution of ca 0.04 cm-1.